From 4ccf991f611b53bc23da9f078acdb9356241074a Mon Sep 17 00:00:00 2001
From: Nick Treleaven <n@trelsoft.com>
Date: Wed, 17 Feb 2021 19:45:11 +0000
Subject: [PATCH] checker: warn when casting a fixed array (use `&arr[0]`
 instead) (#8787)

---
 vlib/builtin/builtin_nix.c.v |  9 +++++----
 vlib/net/tcp_read_line.v     |  3 +--
 vlib/os/os_nix.c.v           | 12 ++++++------
 vlib/os/os_windows.c.v       |  4 ++--
 vlib/v/checker/checker.v     |  2 ++
 vlib/v/util/util.v           |  4 ++--
 vlib/x/websocket/message.v   |  2 +-
 7 files changed, 19 insertions(+), 17 deletions(-)

diff --git a/vlib/builtin/builtin_nix.c.v b/vlib/builtin/builtin_nix.c.v
index 4728ee6199..78904ebc6a 100644
--- a/vlib/builtin/builtin_nix.c.v
+++ b/vlib/builtin/builtin_nix.c.v
@@ -90,8 +90,8 @@ fn print_backtrace_skipping_top_frames_linux(skipframes int) bool {
 			C.tcc_backtrace("Backtrace")
 			return false
 		}
-		buffer := [100]byteptr{}
-		nr_ptrs := C.backtrace(voidptr(buffer), 100)
+		buffer := [100]voidptr{}
+		nr_ptrs := C.backtrace(&buffer[0], 100)
 		if nr_ptrs < 2 {
 			eprintln('C.backtrace returned less than 2 frames')
 			return false
@@ -117,8 +117,9 @@ fn print_backtrace_skipping_top_frames_linux(skipframes int) bool {
 			buf := [1000]byte{}
 			mut output := ''
 			unsafe {
-				for C.fgets(charptr(buf), 1000, f) != 0 {
-					output += tos(byteptr(buf), vstrlen(byteptr(buf)))
+				bp := &buf[0]
+				for C.fgets(charptr(bp), 1000, f) != 0 {
+					output += tos(bp, vstrlen(bp))
 				}
 			}
 			output = output.trim_space() + ':'
diff --git a/vlib/net/tcp_read_line.v b/vlib/net/tcp_read_line.v
index 38cbdeb199..b44fd5f861 100644
--- a/vlib/net/tcp_read_line.v
+++ b/vlib/net/tcp_read_line.v
@@ -34,8 +34,7 @@ pub fn (mut con TcpConn) read_line() string {
 				break
 			}
 		}
-		bufbp := byteptr(buf)
-		line = unsafe { tos_clone(bufbp) }
+		line = unsafe { tos_clone(&buf[0]) }
 		if eol_idx > 0 {
 			// At this point, we are sure that recv returned valid data,
 			// that contains *at least* one line.
diff --git a/vlib/os/os_nix.c.v b/vlib/os/os_nix.c.v
index 7aa500b3ed..368113adc6 100644
--- a/vlib/os/os_nix.c.v
+++ b/vlib/os/os_nix.c.v
@@ -93,8 +93,8 @@ pub fn ls(path string) ?[]string {
 		if isnil(ent) {
 			break
 		}
-		bptr := byteptr(ent.d_name)
 		unsafe {
+			bptr := byteptr(&ent.d_name[0])
 			if bptr[0] == 0 || (bptr[0] == `.` && bptr[1] == 0)
 				|| (bptr[0] == `.` && bptr[1] == `.` && bptr[2] == 0) {
 				continue
@@ -169,8 +169,8 @@ pub fn exec(cmd string) ?Result {
 	buf := [4096]byte{}
 	mut res := strings.new_builder(1024)
 	unsafe {
-		for C.fgets(charptr(buf), 4096, f) != 0 {
-			bufbp := byteptr(buf)
+		bufbp := &buf[0]
+		for C.fgets(charptr(bufbp), 4096, f) != 0 {
 			res.write_bytes(bufbp, vstrlen(bufbp))
 		}
 	}
@@ -210,11 +210,11 @@ pub fn (mut c Command) read_line() string {
 	buf := [4096]byte{}
 	mut res := strings.new_builder(1024)
 	unsafe {
-		for C.fgets(charptr(buf), 4096, c.f) != 0 {
-			bufbp := byteptr(buf)
+		bufbp := &buf[0]
+		for C.fgets(charptr(bufbp), 4096, c.f) != 0 {
 			len := vstrlen(bufbp)
 			for i in 0 .. len {
-				if int(bufbp[i]) == `\n` {
+				if bufbp[i] == `\n` {
 					res.write_bytes(bufbp, i)
 					return res.str()
 				}
diff --git a/vlib/os/os_windows.c.v b/vlib/os/os_windows.c.v
index ad7d119565..31000f21a2 100644
--- a/vlib/os/os_windows.c.v
+++ b/vlib/os/os_windows.c.v
@@ -102,12 +102,12 @@ pub fn ls(path string) ?[]string {
 	// NOTE:TODO: once we have a way to convert utf16 wide character to utf8
 	// we should use FindFirstFileW and FindNextFileW
 	h_find_files := C.FindFirstFile(path_files.to_wide(), voidptr(&find_file_data))
-	first_filename := unsafe { string_from_wide(&u16(find_file_data.c_file_name)) }
+	first_filename := unsafe { string_from_wide(&find_file_data.c_file_name[0]) }
 	if first_filename != '.' && first_filename != '..' {
 		dir_files << first_filename
 	}
 	for C.FindNextFile(h_find_files, voidptr(&find_file_data)) > 0 {
-		filename := unsafe { string_from_wide(&u16(find_file_data.c_file_name)) }
+		filename := unsafe { string_from_wide(&find_file_data.c_file_name[0]) }
 		if filename != '.' && filename != '..' {
 			dir_files << filename.clone()
 		}
diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index 02b1c99dd6..aea289f9db 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -3911,6 +3911,8 @@ pub fn (mut c Checker) cast_expr(mut node ast.CastExpr) table.Type {
 		ft := c.table.type_to_str(node.expr_type)
 		tt := c.table.type_to_str(node.typ)
 		c.warn('casting `$ft` to `$tt` is only allowed in `unsafe` code', node.pos)
+	} else if from_type_sym.kind == .array_fixed && !node.expr_type.is_ptr() {
+		c.warn('cannot cast a fixed array (use e.g. `&arr[0]` instead)', node.pos)
 	}
 	if node.has_arg {
 		c.expr(node.arg)
diff --git a/vlib/v/util/util.v b/vlib/v/util/util.v
index 9943edcf00..d9f32cbb38 100644
--- a/vlib/v/util/util.v
+++ b/vlib/v/util/util.v
@@ -30,7 +30,7 @@ pub fn vhash() string {
 	mut buf := [50]byte{}
 	buf[0] = 0
 	unsafe {
-		C.snprintf(charptr(buf), 50, '%s', C.V_COMMIT_HASH)
+		C.snprintf(charptr(&buf[0]), 50, '%s', C.V_COMMIT_HASH)
 		return tos_clone(buf)
 	}
 }
@@ -98,7 +98,7 @@ pub fn githash(should_get_from_filesystem bool) string {
 	mut buf := [50]byte{}
 	buf[0] = 0
 	unsafe {
-		C.snprintf(charptr(buf), 50, '%s', C.V_CURRENT_COMMIT_HASH)
+		C.snprintf(charptr(&buf[0]), 50, '%s', C.V_CURRENT_COMMIT_HASH)
 		return tos_clone(buf)
 	}
 }
diff --git a/vlib/x/websocket/message.v b/vlib/x/websocket/message.v
index 469f2c2b64..ec843e635f 100644
--- a/vlib/x/websocket/message.v
+++ b/vlib/x/websocket/message.v
@@ -215,7 +215,7 @@ pub fn (mut ws Client) parse_frame_header() ?Frame {
 	mut rbuff := [1]byte{}
 	mut mask_end_byte := 0
 	for ws.state == .open {
-		read_bytes := ws.socket_read_ptr(byteptr(rbuff), 1) ?
+		read_bytes := ws.socket_read_ptr(&rbuff[0], 1) ?
 		if read_bytes == 0 {
 			// this is probably a timeout or close
 			continue